When garments are produced in an industrial setting in which large numbers of garment parts are delivered to work stations where the garment parts are folded and/or assembled and sewn together, it is important that the equipment provided to the worker be fast and accurate in its operation, and that the equipment be constructed and function so that the operator can expediently and easily load the equipment with the garment parts. Also, it is desirable that once the garment parts have been properly placed in position by the worker on the equipment and the equipment is placed in operation that the equipment not only perform the normal sewing functions on the garment parts, but that the sewing functions be performed accurately and rapidly without developing flaws in the work pieces. Moreover, it is desirable that the equipment run independently, i.e., it is automated, so that after the sewing cycle of the equipment begins the machine operator is now allowed to operate two or more similar pieces of equipment at one time by alternately loading the first machine, and as the first machine functions to complete its cycle of operation, to turn and load an adjacent machine.
During the normal sewing function of the continuous edge of a looped end textile work piece, as when forming a hem in the continuous waist edge of a knitted shirt, for example a T-shirt or knit sport shirt, the edge of the work piece is placed in tension, usually by placing the edge portion of the work piece about a pair of spaced guide spindles that rotate and advance the edge portion through the sewing station. At the beginning of the sewing cycle the guide spindles move away from each other so as to lightly stretch, or tension, the edge portion of the work piece, and upon the work piece becoming stretched to a given tension, the cycle of operation of the sewing system begins. Expandable spindle assemblies of this type are disclosed in U.S. Pat. Nos. 4,046,087; 5,437,238; 5,562,060; 5,570,648; 5,522,332; and U.S. patent application Ser. Nos. 08/556,707 and 08/548,585.
The initial tension applied to the work piece by the spindles is selected so as to create the optimum conditions for the sewing function, and the desired conditions are compatible with the work piece and with the operation of the equipment. For example, some textile work pieces might become excessively elongated or might develop excessive curl at the edge of the hem if overstretched. Therefore, the initial tension applied to the work piece usually will be matched with the characteristics of the work piece.
As the sewing machine operates to insert stitches in the textile work piece, for example, while sewing a hem therein, both the needles and the threads which penetrate the work piece move in between, or sometimes even destroy, the yarns of the work piece which tends to move or spread the yarns further apart from one another and thus causes the work piece to progressively lengthen or "grow" during the sewing operation. Additional "growth" in the work piece can be attributed to temporary stretching of the work piece as it travels through a folding guide, if one is provided, and any additional guides provided as a part of the machine. As the product begins to grow, the tension of the work piece as initially applied by the guide spindles of the equipment usually decreases. Unless some adjustment is made to maintain the desired tension in the work piece, as the reduced tension might cause a malfunction in the sewing operation and a flaw in the work piece.
The prior art structures typically have utilized movable spindles for the purpose of accommodating different sized work pieces, so that the spindles could be expanded farther apart to apply proper tension to the larger size garments, yet could be moved closer together to accommodate the smaller size garments. Since the movable spindle concept was well known, the prior art systems have also utilized movable spindles to adjust the tension of the work piece during the cycle of operation of the sewing machine, typically by moving the spindles progressively farther apart during the sewing cycle to maintain the tension in the work piece as the work piece grows.
While the progressive movement of the spindles during the sewing operation can adjust the tension in the work piece, a spindle typically has a relatively large mass and its movement in small increments is difficult to accurately control. When the system attempts to move a spindle, it first must overcome the static friction of the spindle support system, and once this is overcome, the spindle typically is moved in a short surge of movement before its movement can be stopped. Since the work piece is usually looped about the movable spindle, the movement of the spindle results in movement, stretching, of both the upper and lower runs of the work piece, thereby effectively doubling the length of the movement of the work piece for a given movement of the spindle. This intermittent movement tends to continually overstretch, or tension, and then release the work piece.
Therefore, it can be seen that it would be desirable to provide a spindle assembly for a sewing machine which would include the advantages of the types of assemblies described above, but which would further include the ability to automatically maintain a constant tension in the workpiece during the entirety of the sewing operation for maintaining positive control over the workpiece to ensure that a uniform hem, for example, is sewn in each workpiece so processed during the cycles of operation of the sewing machine, without otherwise overstretching or understretching the work piece.
It is desirable for the movable spindle system to be constructed to allow at least one of the work piece handling spindles to be moved closely adjacent the sewing head and work platform so as to accept even the smallest sizes of the work piece, so that small sized work pieces can be manufactured on the sewing system. In some instances, the levers and other elements associated with the movable spindle or spindles form an obstruction to the movement of the spindle or spindles while it is, or they are, respectively, in close proximity to the head of the sewing machine. If the movable spindle(s) cannot move close to the sewing machine, additional stretching of the smaller size garments might be required as they are loaded onto the guide spindles, resulting in extra effort required by the machine operator to accomplish this task, and may possibly result in the overstretching of the work piece.